JPS6022534B2 - Chuyuna - Google Patents

Description

[Detailed description of the invention] The present invention relates to a tuner for a television receiver.

Fig. 1 shows a conventional tuner, in which a UHF tuner 2U consisting of a high frequency amplifier 3U, a mixer 4U and a local oscillator 5U is connected to the UHF antenna IU, and a high frequency amplifier 3V, a mixer 4V and a local oscillator 5U are connected to the VHF antenna IV. A 2V VHF tuner consisting of 5V is connected. The UHF tuner 2U and VHF tuner 2V are so-called electronic tuning tuners that use variable capacitance diodes as tuning elements for high frequency amplifiers 3U, 3V and local oscillators 5U, 5V. When receiving broadcast waves in the VHF band, the UV selector switch 6 is turned off, and the output terminal 7 receives V.
IF (image intermediate frequency) output is obtained. When receiving broadcast waves in the UHF band, the UV selector switch 6 is turned on, and the VIF output of the UHF tuner 2U is output to the mixer 4V.
is guided to the output terminal 7 as an intermediate frequency amplifier. A tuner having the configuration shown in FIG. 2 in which the UHF tuner 2U and VHF tuner 2V are not provided independently in this way has also been proposed.

That is, in FIG. 2, 8 selects the UHF band/・
9 represents a low-pass filter for selecting the VHF band, and the output of the low-pass filter 9 is frequency-converted by a frequency converter 10 into a high-frequency signal in the UHF band. And/・The output of the bus filter 8 and the output of the frequency converter 10 are set to the UV selector switch 6.
The output of the high frequency amplifier 3U is combined with the mixer 4U which receives the output of the local oscillator 5U, and a VIF output is obtained at the output terminal 7. In the conventional tuner mentioned above, the high frequency amplifier 3U, 3
It is necessary to provide a channel selection circuit in the order of input of V, therefore, there are many variable capacitance diodes as variable reactance elements, local oscillator 5U, 5V and high frequency amplifier 3U, 3V.
This has the disadvantage that tracking adjustment performed between the input-side channel selection circuits is troublesome.

In addition, it was necessary to convert the UV cutout and the low channel and high channel in the VHF band. The present invention eliminates the drawbacks of the conventional tuner, and is designed to improve image interference characteristics.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.

In FIG. 3, reference numeral 11 indicates a first mixer, and a received signal in the VHF band or UHF band is supplied from the antenna 1 to the first mixer 11. first mixer 1
1 is a single balanced type consisting of diodes,
A local oscillation output from a first local oscillator 12 is supplied. In the first local oscillator 12, the tuning voltage applied to the variable capacitance diode of the tuning circuit is varied, so that the frequency f of the output of the local oscillator is, for example, 1.4 squares 5 [GHZ
] to 2.1675 [GHZ], and the received signal at frequency fr in the VHF band and UHF band is ~2.1675 [GHZ].
It is converted to a frequency higher than the highest frequency (f2=f, -fr), for example, approximately 1.4 [GH2] as the video carrier frequency, and is sent to the tuned amplifier 14 via the 1.4 GHZ single tuned circuit 13. Supplied. The output of the tuned amplifier 14 is supplied to a second mixer 16 via a double tuned circuit 15. The second mixer 16 is supplied with the output of a local oscillator 17 with a fixed frequency of, for example, 1.3435 [GH2], so that the output terminal 7 is supplied with a fixed frequency of, for example, 1.3435 [GH2].
A VIF output with an image carrier frequency of 25 to 58.75 [MHZ] appears. The above-mentioned tuned amplifier 14 is necessary to improve the noise figure, and the input and output sides of the tuned amplifier 14 are Single tuning circuit 13 and double tuning circuit 15 on each side
is provided. In addition, as shown in Figure 4, UHF
An antenna IU and a VHF antenna IV are provided, and the UHF band reception signal from the high-pass filter 8 and the VHF band reception signal from the low-pass filter 9 are supplied to the mixers 11U and 81V, respectively, and a common antenna is provided for these mixers 11U and 11V. A local oscillator 12 is provided in
It is also possible to obtain a signal of (≠1.4 [GHZ]), select it with the UV changeover switch 6, and send it to the single tuning circuit 13.

In addition, as shown in FIG. 5, the first mixer 11 is commonly used in the UHF and VHF bands, and the local oscillator 2
U and 12V may also be used. Furthermore, as shown in FIG. 6, first mixers 11U and 11V and local oscillators 12U and 2V may be provided corresponding to the UHF band and VHF band, respectively. In this way, if the mixer 11 or the local oscillator 12 is configured separately for each band, the design thereof becomes easier in terms of the frequency characteristics of the tuning transformer, the variable range of the variable capacitance diode, etc. Note that in FIGS. 4 to 6, the configuration after the single-tuned circuit 13 to which the output of the mixer is supplied is the same as that in FIG. 3, and therefore is omitted. According to the present invention described above, "the received signal from the antenna 1 (IU or IV) is supplied to the first mixer 11 (11U or 11V) without going through the channel selection circuit, and the channel selection is performed by the first local oscillator 12. Since this is done by varying the frequency of the output, the number of components including variable capacitance diodes can be reduced compared to conventional configurations, and tracking adjustment is greatly simplified.

Further, in the example shown in FIG. 3, there is no need for a band switching screen, and in the examples shown in FIGS. The interference characteristics are good. This will be explained below. First, in the above embodiment,
The frequency f of the output of the first local oscillator 12, the frequency of the output of the first mixer 11, etc., and the frequency f of the output of the second local oscillator 17.
The relationship between the output of and the frequency f3 is (f3<f2<f,)
There is a relationship between

In this case, a condition is found in which the frequencies of radio waves other than the desired wave among the received signals are not mixed, ie, a condition in which image interference does not occur. Here, since the first mixer 11 is a single-balanced type, "odd-order spurious signals are canceled out, so we only need to consider even-order spurious signals, and we need to consider the 4th-order spurious signal, which is large in level." .First, if the frequency of the undesired radio waves is fr, then 3, f
r, main f2...{1}
If the following conditions are satisfied, image interference will not occur.

Here, if the frequency of the desired wave is fro, then ra=f, -f
ro・...” Since {2}, from formula (1) and formula ■, 2, me fr.

It becomes {3}. Here, the VHF band and UHF band are respectively (9
1.25-221.75 [MHZ] and (471.25
~769.75 [MHZ]), by substituting this value, approximately f. >340 [MHz]……
'41.

Second, even if fourth-order spurious appears in the output of the first mixer 11 due to two undesired radio waves with different frequencies (their respective frequencies are fr and fr2), this will cause image interference. In order not to have 2, soil fr, ±fM main f
2. ．．・・・・・・ Condition '5' must be satisfied.

Even if you do the same thing as above, the key fro fr, 1000 fr2......
[61, so f, > 1450 [M
HZ〕・・・・・・・・・ {7'
becomes.

Third, the conditions under which image interference does not occur due to three undesired radio waves of different frequencies (each frequency is fr, , fr2 and fr3) are f, Fr, ±fr2±f.
r3 sheep f2...... ■ However, since the term f disappears from both sides, there is no condition to satisfy this formula (■).

Further, the above study is based on the above-mentioned embodiment, and the first mixer 11 performs frequency conversion of (fr-f,=f2),
In the second mixer 16, frequency conversion of (f3 - etc.) was performed, but each mixer performs frequency conversion using the sum method of (fr + f, = f2) and (13 + f2). If we conduct the same study as above for the cases where f, > 770 [MHZ]......
[9}, and in the second case, corresponding to equation '7}, f,>2310[MHZ]...OQ.

In the third case, there are no conditions to satisfy. In the above study, only the frequency relationship was considered, but the level is also considered. In other words, since the navy blue diode constituting the first mixer 11 can be covered with 1=L(ewani-・), the injection voltage should be set to V.
o, if the signal voltage is Vs and the series is expanded, 1=e magazine v
.

(10 belts vs + 2! Hide VS 20...) and Surasu'ma (magazine v8 state change) If you can no longer ignore it (when the input becomes larger), it will suddenly become worse.

Therefore, there is no need to consider cases where (magazine v3) is negligible compared to 1.

Taking this point into consideration, in the third case described above, since the beat is caused by three signals and the signal level is low, image interference is not a problem. Therefore, if the oscillation frequency of the first local oscillator 12 satisfies the relationship of the '71 formula or the 00 formula, it is possible to prevent image interference from occurring. The above embodiment also has a frequency relationship that satisfies the relationship of equation {7). Of course, this frequency is within a range that is sufficiently practical with currently available devices. However, in reality, the maximum received field strength in the VHF band is 110 (ship), and the maximum received field strength in the UHF band is 100 (ship), so considering these actual circumstances, the second case mentioned above The problem of image interference can be solved to a certain extent if only the first case, ie, formula {4) or formula (2), is satisfied without considering the above. Thus, by selecting the frequency of the output of the first mixer 11 to be equal to or higher than the highest frequency (7 MHz) of the received signal, a tuner with good image interference characteristics can be realized. In addition, the above-mentioned example is VH in Japan.
Although the frequency relationship is defined for received signals in the F and UHF bands, it can be applied to received signals in other frequencies with similar benefits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of a conventional tuner, FIG. 2 is a block diagram of another example of a conventional tuner, FIG. 3 is a block diagram of an embodiment of a tuner according to the present invention, and FIGS.
The figures are block diagrams of main parts of other embodiments of the present invention. 1, IU, IV are antennas, 11$11U, 11V are first mixers, 12, 12U, 12V are first local oscillators, 14 is a tuned amplifier, 16 is a second mixer.
is the second local oscillator. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A received signal over the VHF and UHF bands is supplied to a first mixer which is given the output of a first local oscillator whose frequency is variable, without going through a tuning circuit, and the output of the first mixer is fed to the frequency range via a tuned amplifier. The output of the fixed second local oscillator is supplied to a second mixer, so that a video intermediate frequency signal is obtained at the output of the second mixer, and the frequency of the output of the first mixer is the same as the received signal. A tuner in which the frequency of the output of the first local oscillator is varied so as to be equal to or higher than the highest frequency of the tuner.